1. Field of the Invention
The present invention relates to a mold monitoring apparatus for an injection molding machine, which apparatus captures an image of a cavity portion of an opened mold, and determines the state of the cavity portion by means of image processing.
2. Description of the Relevant Art
Conventionally, there has been known a method of capturing, by use of a video camera, an image representing the state of a mold, and comparing the brightness of the captured image with that of a previously stored reference image in order to determine whether a molded article is present or absent within the mold. However, this method involves a problem in that when the brightness (brightness level) in a space surrounding a molding machine varies due to on and off of electric lights or influence of external light, the method erroneously determines a normal state to be anomalous, or an anomalous state to be normal.
In order to solve the above-described problem, there has been proposed a mold monitoring apparatus (monitoring method) for an injection molding machine, which apparatus (method) captures an image of a cavity portion of an opened mold, and determines the state of the cavity portion by means of image processing (see Japanese Patent Application Laid-Open Open (kokai) No. 63(1988)-126718).
In the monitoring method disclosed in the publication, an image of a mold is divided into pixels; brightness of each pixel is detected; the image is then binarized; i.e., converted to a black-and-white image, while a previously set binarization brightness level is used as a reference; and the thus-obtained binarized (black-and-white) image is compared with a previously stored binarized image representing a normal state, wherein the darkest brightness level among all the pixels of the detected image is determined; when the darkest brightness level falls outside an allowable range previously set for darkest brightness level, injection molding operation is stopped; when the darkest brightness level falls within the allowable range, the darkest brightness level of the detected image is compared with the darkest brightness level among all the pixels of the previously stored image of the normal state; and when the level difference is greater than an allowable value, the previously set binarization brightness level is corrected; i.e., increased or decreased in accordance with the level difference, in order to properly perform binarization of the detected image.
However, in the above-described conventional monitoring method (monitoring apparatus) the following problems remain to be solved.
First, because of its operating principle, the conventional method (apparatus) cannot avoid influences of changes in brightness in a space around the molding machine. Therefore, erroneous operation cannot be completely avoided, and this imposes a limit on enhancement of reliability and safety.
Second, since influence of brightness is corrected at the time of image processing, extra processing must be performed, possibly resulting in impaired processing accuracy.